Hanson endorses the brain emulation scenario as the most plausible near term route to AI. I agree with this, primarily because Nature has already done so much work to optimize the human brain. I doubt that we will get very far with AI in the near term without exploiting the one existing model at our disposal. (Note, "most plausible" does not mean I think we'll accomplish brain emulation in the next 50 years. It might well take much longer, even though raw computational power will be sufficient.)
... evolution has compressed a huge amount of information in the structure of our brains (and genes), a process that AI would have to somehow replicate. A very crude estimate of the amount of computational power used by nature in this process leads to a pessimistic prognosis for AI even if one is willing to extrapolate Moore's Law well into the future. Most naive analyses of AI and computational power only ask what is required to simulate a human brain, but do not ask what is required to evolve one. I would guess that our best hope is to cheat by using what nature has already given us -- emulating the human brain as much as possible.
Below is a nice summary of long term trends in human population and economic growth, from this Hanson paper.
Humans (really our human-like ancestors) began with some of the largest brains around, and then tripled their size. Those brains, and the innovations they embodied, seem to have enabled a huge growth in the human niche - it supported about ten thousand humans two million years ago, but about four million humans ten thousand years ago.
While data is scarce, this growth seems exponential, doubling about every two hundred and twenty five thousand years, or one hundred and fifty times faster than animal brains grew. (This growth rate for the human niche is consistent with faster growth for our ancestors - groups might kill off other groups to take over the niche.) About ten thousand years ago, those four million humans began to settle and farm, instead of migrating to hunt and gather. The human population on Earth then began to double about every nine hundred years, or about two hundred and fifty times faster than hunting humans doubled.
Since the industrial revolution began a few hundred years ago, the human population has grown even faster. Before the industrial revolution total human wealth grew so slowly that population quickly caught up, keeping wealth per person at a near subsistence level. But in the last century or so wealth has grown faster than population, allowing for great increases in wealth per person.
Economists' best estimates of total world product (average wealth per person times the number of people) show it to have been growing exponentially over the last century, doubling about every fifteen years, or about sixty times faster than under farming...